The invention relates to the processing of semiconductor wafers having epitaxially-deposited layers thereon.
U.S. Pat. No. 3,718,514 to W. C. Erdman and P. Miller discloses the problems associated with the growth of projections, also referred to as spikes, on semiconductor wafers during the formation thereon of epitaxial layers. The occurrence of projections stems generally from nucleation sites such as particles and crystallographic perturbations. Their suppression during the epitaxial growth process is costly and an economical removal method is preferred. The above-noted patent also discloses a technique for the selective removal of such projections by selective etching using a photoresist masking layer over an oxide layer.
Although this earlier technique has provided a considerable advance in the fabrication art it has been found that the random occurrence of pinholes in the photoresist film results in unwanted etch pits, referred to as extraneous etch pits. Projection etch pits referred to hereinafter are etch pits present in the wafer surface, after projection removal, at the identical site of an epitaxial projection. In some instances, using the photoresist film technique has resulted in a greater density of extraneous etch pits than of projection etch pits. Moreover, the use of the photoresist film is attended by undue complication and the possibility of added organic contamination during its formation and removal.
Efforts to remove the projections solely by mechanical means have been largely unsuccessful or, where moderately successful, have been excessively costly, involving practically hand operations. Accordingly, there is a need for a sure and simple method of projection removal which can be practiced effectively without introducing additional damage to the semiconductor wafer.